The field of this invention relates to welding of separate metallic cylindrical pipes and more particularly to a supporting apparatus for the welding head to cause the welding head to move about the pipe to produce the desired weld.
It has long been known to use various types of welding head supporting devices for the welding of pipes of various diameters. Generally each welding head supporting structure is designed for a specific diameter of pipe. Welding of one section of pipe to another section of pipe is normally performed repetitively. Therefore, it is frequently common to construct a welding head supporting assembly for a specific diameter of pipe. Each welding head supporting assembly is designed not to accommodate various pipe diameters.
The reason that welding head supporting structures have been designed for specific diameters of pipes is that the welding head must be rigidly mounted with respect to the pipe. Any minor amount of movement between the welding head supporting structure and the pipe will frequently result in the producing of an inferior weld. Also, it is generally desirable to have the welding head supporting structure to be continuous with no gaps. The welding head supporting assembly must be frequently movable from one pipe to another pipe and when installed on the new pipe, the break area of the welding head supporting assembly should be completely closed and again rigidly mounted onto the new pipe.
However, pipes of a given diameter vary slightly in diameter. In a larger diameter pipe, this variation can become substantial. Therefore, some structure must be utilized within the welding head supporting assembly to compensate for this pipe diameter variation.
In the past, it has been common to utilize a flexible band in conjunction with the welding head supporting assembly with this band to be mounted about the pipe to be welded. In the past, in order to compensate slightly for variations in pipe diameters, it has been known to have the ends of the band not quite meet, but have a slight gap therebetween. By increasing or decreasing the size of this gap, this band can then be utilized to accommodate slight variances in pipe diameters. However, when the welding head is moved across this gap area, there may result a momentary hesitation in the welding head, or a momentary increase in speed. This hesitation or increase in speed may result in the production of an inferior weld. It is well-known that only one small inferior spot of a weld that is several feet long will result in the production of an inferior weld.
Also, in the past, there has been utilized a spring-biased foot pad assembly between the band and the pipe. These spring-biased foot pads are for the purpose of compensating for slight variation in pipe diameter. Although these foot pad assemblies do work satisfactory with small variations in pipe diameter, it has been found that extreme variations in pipe diameter cannot be compensated for with the spring-biased foot pad assemblies used in the past.